Structural and regulatory differences in amylase isoenzymes in germinating Brazilian barley cultivars

Abstract

The amylase electrophoretic patterns of 10 Brazilian brewing-barley varieties with different malting grades and diastatic power were analyzed during the 7-day germination which occurs during the malting process. Intra and inter-variety genetic variability was observed at both the structural and regulatory level. In the first few days after germination all varieties showed a few active loci, all of them with low activity. In subsequent days, new loci became active and those already detected since early germination showed increased activity. All varieties showed a continuous increase in amylase synthesis until the 3rd and/or 4th day after germination. Some varieties maintained high amylase activity until the last day of germination, while others showed a decrease in activity on the 5th or 6th day. No specific band increased or decreased its intensity independently of the others. A total of 14 loci were detected, out of which only one locus was polymorphic, indicating very low structural genetic variability, with only 2.8% polymorphic loci, an average of 1.04 alleles per loci, and an average expected heterozygosity of only 0.7%. The mean intra-variety Jaccard similarity coefficient complement (1 - SJ) was 0.009. The mean intra-variety difference based on regulatory differences was higher (1 - SJ = 0.17) than that obtained based on structural differences, suggesting differential gene activation. Inter-variety differentiation also showed low structural variability, with 1 - SJ = 0.026 and a Nei genetic distance (D) value of 0.0076, and a remarkable increase in divergence caused by differential gene activation (1 - SJ, = 0.34). These results indicate that regulatory polymorphism is the principal agent responsible for amylase variability in the barley varieties analyzed.